Field of the Invention
This invention pertains generally to the field of aircraft vision systems that present flight information to the pilot or flight crew of an aircraft.
Description of the Related Art
It is well-known that a Synthetic Vision System (“SVS”) may generate image data representative of a synthetic, three-dimensional perspective of a scene in front of the aircraft. When provided to a display system, the synthetic image could be presented on the screen of a display unit. In addition, it is well-known that an Enhanced Vision System (“EVS”) may generate image data representative of the real-world as an enhanced image of the scene in front of the aircraft, where such image data has been acquired by one or more fixed or steerable forward-looking image capture devices.
One purpose of the EVS is to provide imagery of the terminal area and runway environment to the flight crew during times when meteorological conditions prevent the crew from seeing the runway environment with natural, unaided vision. So, the EVS imagery can improve the situation awareness of the flight crew during the performance of instrument approach procedures.
Sensors employed in an EVS may generally fall into two categories: passive sensors and active sensors. Passive sensors may receive electromagnetic energy from the environment and may include visible light and infrared cameras. Active sensors may transmit electromagnetic energy into the environment and then receive electromagnetic energy reflected from the environment; a radar system is a common active sensor. Generally, passive and active sensors operate in different ranges of the electromagnetic spectrum. As such, passive sensors are subject to interference (i.e., an absorption of energy) from different meteorological conditions as compared with active sensors. The use of both passive and active sensors in an EVS may increase the availability of the system, for instance, by decreasing the odds that the EVS cannot produce an image to present to the crew.
Passive sensors such as cameras may produce video images captured from the point of view of the sensor. If the passive sensor is installed in an appropriate place on the nose of an aircraft, the pilot can be presented with a video image that is very nearly the same as his or her point of view through the cockpit windows.
Generally, an active sensor does not generate the same kind of video images produced by passive sensors. Instead, the active sensor transmits energy into the outside world and measures reflected energy from the outside world. The active sensor then maps the reflected energy into a three-dimensional (“3-D”) model with reference typically made to a polar coordinate system. This three-dimensional data can then be rendered into an image that is very much like the image produced by the passive sensor.
Since active sensor data is captured in a 3-D model, there is an opportunity for active sensors to produce radar-based video imagery with a different point of view of the outside world than is produced by passive sensors. For example, the classic weather radar system generates a 3-D model of the reflectivity of a thunderstorm from which a top-down view the weather system may be generated. The top-down view could be presented on an electronic moving map so that the crew sees the weather system in the context of the flight plan, the location of navigation aids, and the location of other traffic that are also presented on the electronic moving map.
The Radio Technical Commission for Aeronautics (“RTCA”), Inc. has published a Document (“DO”) identified as RTCA DO-341 and entitled “Minimum Aviation System Performance Standards (MASPS) for an Enhanced Flight Vision System to Enable All-Weather Approach, Landing, and Roll-Out to a Safe Taxi Speed,” which is incorporated by reference in its entirety. DO-341 defines high level requirements for implementing an enhanced flight vision system (“EFVS”) to allow landing and rollout operations of aircraft in low visibility conditions of a runway visual range (“RVR”) of 300 feet; although the meanings underlying the terms EVS and EFVS are nearly synonymous, those skilled in the art understand that the two terms are not necessarily identical to one another. As embodied herein, an EVS may be considered as any system (which could include an EFVS) for generating an enhanced image presentable on a Head-Up Display (“HUD”), a Head-Down Display (“HDD”), or any other properly-configured display unit with or without symbology being included.
At the time of this writing, the minimum architecture suggested in DO-341 includes: (1) dual image sensors to generate images of the runway environment, (2) dual HUDs to present images to the pilot flying (“PF”) and pilot monitoring (“PM”), and (3) dual HDDs to present images to the PF and PM. Also, DO-341 assumes that the HUD is essential for the PF to maintain control of the aircraft. If the HUD of the PF fails, control of the aircraft must transition to the PM who must have a functional HUD. The HDDs are back up display devices.
The minimum architecture suggested by DO-341 may be deficient or inadequate to meet the expected system availability and integrity requirements to support landing and rollout operations in the low visibility conditions of 300 feet RVR. The deficiencies in the architecture may include, but are not limited to, (1) an inability to detect and isolate system faults is a dual sensor system (i.e., the system cannot vote between numerous sensors to determine if any specific sensor has failed), (2) a failure of the entire EVS if one-sensor EVS is used, where changing meteorological conditions may block the part of the range of electromagnetic spectrum which the sensor is configured to detect (e.g., fog rolls in and dual infrared camera can no longer see the runway), and (3) an inability of a PF or a PM to verify the integrity of the enhanced vision image (or enhanced image) generated by the EVS when the PF or PM cannot see the outside world and, therefore, loses his or her basis to verify the integrity of the enhanced image.